Depending on your seating position. Some chairs are lower than the table, causing your wrist to 'bend' when using the mouse, which thick mousepad will be a problem because the edge will 'poke' your wrist. Probably medium (4mm) or thin (2mm) cloth based pads are good. You can try brands like Steelseries QCK or Razer Goliathus . Brands like Roccat and CM Storm are the alternatives.

Weird, the shape of the extended is based on the width. I doubt there is any that wide, but you can try Steelseries QCK+ there are limited edition versions as well.